1. Field of the Invention
The present invention relates to a light apparatus control system for a vehicle.
2. Description of Related Art
A known light apparatus control system installed in a vehicle measures a light intensity (illuminance) of ambient light applied from outside of the vehicle and turns on light apparatuses (e.g., headlamps) of the vehicle when the light intensity of the ambient light is decreased below a light-on threshold value. In such a light apparatus control system. It is desirable to turn on the light apparatuses of the vehicle as fast as possible at the time of entering an inlet of a tunnel and to keep an off-state of the light apparatuses of the vehicle at the time of passing through a road area under a covering object, such as an elevated bridge where the turning on of the light apparatus is not necessary.
In a case of Japanese Patent No. 2949627B2, besides an absolute value of the light intensity of the ambient light applied from outside of the vehicle, a slope of change (gradient of change) in the light intensity of the ambient light from the bright state to the dark state is measured. When the slope is steep, i.e., when the light intensity of the ambient light is decreased rapidly, it is determined that the vehicle has entered the road area under the covering object (e.g., the tunnel or elevated bridge), and the light-on threshold value is decreased. In this way, flashing (instantaneous turning on and off) of the light apparatuses on the road area under the elevated bridge is prevented.
Furthermore, the light apparatus control system of the vehicle recited in Japanese Unexamined Patent Publication No. 2005-199974A (corresponding to US 2005/0157509A1) has an upper light intensity sensor and a front light intensity sensor. The upper light intensity sensor measures a light intensity of ambient light, which is applied to the upper light intensity sensor from the upper side of the vehicle. The front light intensity sensor measures a light intensity of the ambient light, which is applied to the front light intensity sensor from the front side of the vehicle. The light apparatus control system of Japanese Unexamined Patent Publication No. 2005-199974A detects presence of the tunnel when the light intensity of the ambient light, which is measured with the front light intensity sensor, is decreased below a predetermined value. When the presence of the tunnel is detected, the light-on threshold value is increased (raised), so that the light apparatuses can be turned on quickly.
As discussed above, in the case of Japanese Patent No. 2949627B2, the light-on threshold value is reduced in the case where the slope of the light intensity of the ambient light outside of the vehicle is steep at the time of decreasing of the light intensity, so that the flashing of the light apparatuses in the road area under the elevated bridge is prevented. However, in general, the brightness of the illumination at the inlet of the modern tunnel is increased in view of the dark adaptation of human eyes. Therefore, when the light-on threshold value is decreased, the light apparatuses of the vehicle may not be turned on. Furthermore, the low light intensity of the ambient light at, for example, the dusk time (sunset time) and the low vehicle speed caused by, for example, traffic jam should be concerned. In these cases, when the vehicle enters the road area under the elevated bridge, the rapid decreasing change in the slope of the light intensity of the ambient light cannot be detected, so that the flashing of the light apparatuses of the vehicle cannot be prevented.
In the case of Japanese Unexamined Patent Publication No. 2005-199974A (corresponding to US 2005/0157509A1), the presence of the tunnel is sensed when the light intensity of the ambient light, which is measured with the front light intensity sensor, is decreased below the predetermined value. When the presence of the tunnel is detected, the light-on threshold value is increased, so that the light apparatuses can be turned on quickly. However, the decrease of the light intensity of the ambient light, which is applied from the front side of the vehicle, occurs not only at the time of entering the tunnel but also at the time of passing through the road area under the covering object, such as the elevated bridge, where the turning on of the light apparatuses of the vehicle is not required, or at the dusk time. In these cases, the decrease of the light intensity of the ambient light applied from the front side of the vehicle is not smaller than that of the time of entering the tunnel. Accordingly, it may be possible to distinguish the tunnel from the elevated bridge and the dusk time. However, it is not possible to distinguish between the elevated bridge and the dusk time. Therefore, it may not be possible to appropriately perform the control operation to maintain the turning off of the light apparatuses of the vehicle in the road area under the elevated bridge and to turn on the light apparatuses of the vehicle at the dusk time.